How do you calculate the radius of a slot port?

[akuma4u]

pardon my crappy math skills,.. but how do you calculate the radius of a slot port? lets say for example 12 inches tall x 2.75 inches wide? what would the radius be?

i need to figure out how to do radius calculations in order to figure out port velocity using this calculator http://www.carstereo.com/help/Articles.cfm?id=4

[Markous]

You wouldn't be calculating radius (thats just for circles)  just area by multiplying height times width.

Which in your case would be 33 inches square.

 

edit - That would be the equivalent of a 6.5" diameter round port if i did the math right

 

 

 

[WalledSonic]

You mean like a 90 degree bend around the edge of the box?

[akuma4u]

the link i provided with the calculator, is that only for aero ports? or can that be used for slot ports? if so ,. what do i enter in the area where it says radius?

[akuma4u]

i have several designs which i need figuring out the port velocity on to make sure its under 7-8% ... but i dont know how.. can someone help me out?

[WalledSonic]

So take your H x W dimension, then divide it by pi, then take the square root of that.  That will be effective radius. 

Example: 4" x 8" port = 32 sq inches area

(pi) x R^2 = area

(pi) = 3.14159

32/3.14159 = 10.186.  Take the square root.  That equals 3.192.  Use R = 3.192 for this example.

[Markous]

The difference in surface area wouldn't allow you to use that same number in that particular calculation though would it Walled?

[WalledSonic]

5 minutes ago, Markous said:

The difference in surface area wouldn't allow you to use that same number in that particular calculation though would it Walled?

No, but the calculation isnt gonna net you an exact response in the first place.  At least OP can be consistent.  The difference in drag shouldnt change tuning more than a frequency or two, I'd imagine.

Term pro software said my design tuning was 33Hz.  Its actually 26Hz.  So even software wont get you exactly where you need to be. 

EDIT: I know OP is talking port velocity, but same thing goes.  Its not gonna be exact, especially with different power levels.  

[akuma4u]

walledsonic: using your explanation (thanks) i entered in my port h x w.. 12 x 2.75 and in the end i got 2.87 for the radius.. i entered this into the calculator and i got the answer: 2.13 percentage of mach

now this is under the 7-8% number i was told to keep it under , so this should be fine right? OR should the answer read .8 or less?

[WalledSonic]

Dont know if this will help Akuma.